The ability of ultrasound measurements to predict new born volume and weight will be determined. Two basic methods will be compared: A series of simple measurements combined in a multiple regression against birth weight, and volume measurements made by means of a three-dimensional reconstruction of the fetus as a series of ultrasonic cross-sections. The simple measurements to be used are transverse abdominal circumference, skull circumference, biparietal diameter and long axis. The long axis end-points and three-dimensional reconstruction will be determined by means of a real-time scanner coupled to a three-dimensional position locating system. Computer programs have been developed which construct a perspective display of scans randomly oriented to each other and which use the reconstruction to find volume. Bench studies on this sytstem are accurate to 5%. If such accuracy can be obtained with the fetus, this technique could be used to investigate weekly growth and assess well-being.